1. Field of the Invention
The present invention relates to a power unit for a motorcycle, and more particularly to a motorcycle power unit which includes a hydraulically-operated continuously variable transmission, also known as CVT. While riding such a vehicle, it may be necessary to tilt or bank the motorcycle to one side or the other. Any structures, such as a water pump, protruding laterally outwardly from the vehicle could be damaged in such a steep banking maneuver. The overall balance of the motorcycle is also influenced by such protruding members.
2. Description of the Background Art
A number of power units including CVT transmissions have been applied to motorcycles. For an example, it has been known to provide a motorcycle power unit including an engine with a crankshaft, a drive pulley shaft and an integrated V-belt-type automatic transmission including a driven pulley shaft, and an output shaft which outputs power to a rear drive wheel. Such a motorcycle power unit includes a water pump which circulates cooling water for the inside of the engine, where the water pump is provided with a drive mechanism.
For example, Japanese published patent document JP-A-2001-65650 (page 2, FIG. 3—also published as JP Pat#3823630 to Shinobu) discloses a motorcycle power unit including a V-belt driven automatic transmission. In the engine disclosed in the Shinobu reference, the drive shaft, crankshaft, and output shaft are arranged parallel to each other.
In addition, it is known that any components extending laterally outwardly from the motorcycle engine will affect the banking ability of the vehicle, since during a steep banking turn, such outwardly extending components may contact the ground and become damaged. (As used herein, the term “banking” refers to leaning during turns). Thus, it is desirable to limit the number and type of these laterally extending members to prevent damage to them and to the motorcycle. In addition, since the weight and height of the engine will affect the center of gravity of the motorcycle, it is desirable to have a compact, lightweight engine.
With respect to some known motorcycle power units of this type, the water pump is mounted on an end of the drive pulley shaft. Accordingly, compared with an engine which mounts a water pump on a shaft other than the drive pulley shaft, additional drive parts for the pump and an arrangement space for the pump become unnecessary and, the engine can be made smaller and more compact. On the other hand, in this known arrangement, the water pump projects laterally outwardly from a side surface of the engine and therefore, there exists a possibility that the bank angle and balance of the vehicle is adversely affected by such an arrangement.